If the king "agrees" in being extracted, then follows the check with the white queen in b5. The black king will have three choices: 1) Kc8,to get immediately mated by the white rook (Rb8); 2) Kd6, to get immediately mated by the white queen coming to d5 (Qd5); 3) Ke6, trying to escape along a corridor between its own black pawns and the "forbidden rank" swept by the white queen. Bringing the white knights to the fourth rank, first with Nf4+ and then Ne4#, you'll complete the job. Knight checks restrict the choices of the defense to capture or flight, since interposing a piece doesn't work. Knight checks, then, restrict changes in the position, during the chase to the king. I hope I may be right and may help you.

i beat it in the second try. The answer is for white : Bc6+,Bxd7+, Rb8+,Qb5+,Qxc6#

Thought about Qd5+ for first move,which would have forced Kh8,then checking with Rf8...RxRf8,but then I could not mate with Qg8,or Qd8,because KxQg8,and Nc6xQd8, so I checked 1.Qf7...Kh8, 2.Qf7+...RxQf7, 3.RxRf7,nice puzzle felt good to solve,Thank's. Opp's,this post was for puzzle winner 5775 posted